KR20070095993A - Base station implementing a physical layer automatic repeat request - Google Patents

Abstract

A base station implementing physical layer automatic repeat request includes a transmitter (38) and a receiver (52). The transmitter has a physical layer transmitter for receiving data, format the received data into packets transmitting the packets and retransmitting packets in response to failure to receive a corresponding acknowledgment for a given packet; an acknowledgment receiver (56) for receiving the corresponding acknowledgment; and an adaptive modulation and coding controller for collecting retransmission statistics and adjusting the particular data encoding/modulation using the collected statistics. The receiver (52) has a physical layer receiver for demodulating the packets; a combiner/decoder (50-1-50-n) for buffering, decoding and detecting packet errors; and an acknowledgment generator for generating an acknowledgment for each packet if that packet has an acceptable error rate.

Description

A base station that implements the automatic retransmission request of the physical layer {BASE STATION IMPLEMENTING A PHYSICAL LAYER AUTOMATIC REPEAT REQUEST}

TECHNICAL FIELD The present invention relates to a wireless communication system, and more particularly, to an improved wireless communication system employing an Automatic Repeat ReQuest (ARQ) scheme of a physical layer (PHY).

Based on the application of High Speed Downlink Packet Access (HSDPA) scheme, Single Carrier-Frequency Domain Equalization (SC-FDE) scheme or Orthogonal Frequency Division Multiplexing (OFDM) scheme A broadband fixed wireless access (BFWA) communication system using any one of Orthogonal Frequency Division Multiplex (orthogonal frequency division) plans has been proposed. An application of this HSDPA scheme would be to transmit downlink packet data at high speed. In this broadband fixed wireless access (BFWA) communication system, buildings or groups of buildings are connected in either wireless or wired manner and operate as a single subscriber location. In such a system, data requirements are very high for multiple end users in a single location that require large bandwidth.

The proposed system employs a layer 2 automatic retransmission request (ARQ) system. Data blocks that were not sent to the subscriber are buffered and retransmitted from Layer 2. Data blocks stored in Layer 2 are typically large data blocks and are transmitted for high signal to noise ratio (SNR) reception, received at a low block error rate (BLER), and rarely retransmitted. In addition, ARQ signaling in Layer 2 is typically slow and requires large buffers and long retransmission intervals.

Thus, there is a need for an alternative system in addition to the layer 2 automatic retransmission request (ARQ) system.

The automatic retransmission request system of the physical layer includes a transmitter and a receiver. At the transmitter, the physical layer transmitter receives the data and formats the received data into specific encoding / data modulation packets. The transmitter of the physical layer includes an n-channel for transmitting a packet and resending the packet in response to not receiving a corresponding acknowledgment (ACK) for a given packet. The transmitter's adaptive modulation and coding controller collects retransmission statistics and uses the collected statistics to adjust specific encoding / data modulation. The receiver has an n-channel receiver of a physical layer that receives the packet. The receiver includes an n channel hybrid ARQ combiner / decoder for combining packet transmissions, decoding packets, and detecting packet errors. The receiver has an acknowledgment transmitter that sends an acknowledgment for each packet if the packet has an acceptable error rate. The receiver includes a sequential delivery element that delivers an acceptable packet to the upper layer.

According to the present invention, an improved wireless communication system employing an automatic retransmission request (ARQ) scheme of a physical layer (PHY) that requires a large buffer and a long retransmission interval can be realized.

1A and 1B show downlink physical layer ARQ 10 and uplink physical layer ARQ 20, respectively.

The downlink physical layer ARQ 10 includes a base station 12 that receives a packet from a higher layer ARQ transmitter 14a provided within the network 14 . Packets from the higher layer ARQ transmitter 14a are applied to the physical layer ARQ transmitter 12a in the base station 12. The physical layer ARQ transmitter 12a encodes the data into a forward error correction code (FEC), adds an error check order (ECS), and puts the data into the state indicated by the adaptive modulation and coding (AMC) controller 12c. The AMC controller 12c can be modulated using binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), or quadrature quadrature amplitude modulation (QAM) (i.e., 16-QAM or 64-QAM). Is performed. In addition, in the orthogonal frequency division multiple access (OFDMA) scheme, the AMC controller 12c may change the subchannel used to carry packet data. The physical layer ARQ transmitter 12a sends a packet to the subscriber unit 16 via the air interface 14 via a switch, circulator or duplexer 12d and antenna 13. In addition, the physical layer ARQ transmitter 12a temporarily stores a message for retransmission in a buffer memory integrated in the physical layer ARQ transmitter 12a, if necessary.

The antenna 15 of the subscriber unit 16 receives the packet. The received packet is input to the physical layer ARQ receiver 16a via a switch, circulator or duplexer 16b. Packets received at the physical layer ARQ receiver 16a are subjected to forward error correction code (FEC) decoding and checking for errors using an error checking sequence (ECS). The physical layer ARQ receiver 16a then receives a packet with an acceptable error rate, ACKs or withholds a positive response signal, or preferably transmits a negative acknowledgment (NAK) signal for retransmission. Control the acknowledgment (ACK) transmitter 16c to request.

The * ACK is transmitted by the ACK transmitter 16c to the base station 12 through the switch 16b and the antenna 15. The ACK is transmitted to the antenna 13 of the base station 12 via the air interface 14. The received ACK is processed by the ACK receiver 12b in the base station 12. The ACK receiver 12b forwards the ACK / NAK to the adaptive modulation and coding (AMC) controller 12c and the physical layer ARQ transmitter 12a. The adaptive modulation and coding (AMC) controller 12c uses the statistics of the received ACK to analyze the channel quality for the subscriber unit 16 and, as described in more detail below, an FEC for continuously sending a message. Encoding and modulation techniques can be changed. If the subscriber unit 16 ACKs the reception of the packet, the original packet temporarily stored in the buffer memory by reception of this ACK at the base station 12 is cleared in preparation for the next packet.

If no ACK is received or a NAK is received, the physical layer ARQ transmitter 12a retransmits the original message or an optionally modified version of the original message to the subscriber unit 16. The retransmission at the subscriber unit 16 is combined with the original transmission if available. This technique facilitates the receipt of accurate messages by the use of data redundancy or optional iterative combining. Packets with an acceptable error rate are sent to higher layer 16d for further processing. The acceptable received packet is delivered to the upper layer 16d in the same data order in which data is supplied to the physical layer ARQ transmitter 12a in the base station (ie, non-sequence delivery). The maximum number of retransmissions is limited to integer values defined by the operator, such as values in the range 1-8. After the maximum number of retransmissions have been attempted, the buffer memory is cleared for use by the next packet. Decoding the ACK using small packets at the physical layer reduces transmission delay and message processing time.

Since PHY ARQ occurs at the physical layer, the maximum number of retransmission occurrences for a particular channel's retransmission statistics is a good measure of its channel quality. Using the retransmission statistics, the AMC controller 12c can change the modulation and coding scheme for that channel as shown in FIG. In addition, the retransmission statistics may be combined with other link quality measurements such as bit error rate (BER) and block error rate (BLER) by the AMC controller 12c to measure channel quality and determine whether a change in modulation and coding scheme is required. May be combined.

To describe a Single Carrier-Frequency Domain Equalization (SC-FDE) scheme, the occurrence of retransmission for a particular channel is measured to provide retransmission statistics (60). A determination as to whether to change the modulation scheme is made using the retransmission statistics (62). If retransmission is excessive, then stronger coding and modulation schemes are typically used 64 at a reduced data rate. The AMC controller 12c can increase the spreading factor and use more code to transmit packet data. Optionally or additionally, the AMC controller may switch from a high data throughput modulation scheme to one lower scheme, such as 64-QAM to 16-QAM or QPSK. If the rate of retransmission is low, a switch from QPSK to a high performance modulation scheme such as 16-ary QAM or 64-ary QAM is made (66). The decision preferably utilizes both the retransmission rate and other link quality measurements signaled from the receiver, such as bit error rate (BER) or block error rate (BLER) (62). The determination limit is preferably set by the system operator.

In the Orthogonal Frequency Division Multiple Access (OFDMA) scheme, retransmission occurrences are used to monitor the channel quality of each subchannel. If the retransmission rate or retransmission rate / link quality for a particular subchannel indicates a poor quality, that subchannel may be selectively nulled from the OFDM frequency set to exclude the use of the bad quality subchannel for some future period. (64). If the retransmission rate or retransmission rate / link quality indicates a high quality, previously nulled subchannels may be added back to the OFDM frequency set (66).

Using retransmission generation as a reference for AMC, flexibility can be provided so that the modulation and encoding method can be matched to the average channel condition of each user. In addition, the retransmission rate is insensitive to measurement errors and reporting delays from the subscriber unit 16.

The uplink PHY ARQ 20 is similar in nature to the downlink PHY ARQ 10 and consists of a subscriber unit 26, wherein packets from the upper layer ARQ transmitter 28a of the upper layer 28 are physical layer ARQ transmitters. Forwarded to 26a. The message is sent to the base station antenna via switch 26d, subscriber antenna 25 and air interface 24. Alternatively, the AMC controller can vary the modulation and coding method using the channel retransmission statistics.

Similar to the physical layer ARQ receiver 16a of FIG. 1A, the physical layer ARQ receiver 22a determines whether the message has an acceptable error rate that requires retransmission. The ACK transmitter reports the status to the subscriber unit 26 so that the physical layer ARQ transmitter 26a is temporarily stored in the physical layer ARQ transmitter 26a that is preparing to receive the next message from the higher layer 28. Retransmit or optionally clear. Receive packets are successfully sent to the network 24 for further processing.

Although not shown for brevity, the system is well available for HSDPA applications in BFWA systems, although other implementations may be available. The BFWA system may use frequency division multiplexing or time division multiplexing SC-FDE or OFDMA. In such a system the base station and all subscribers are in a fixed location. The system may include a base station and a plurality of subscriber units. Each subscriber unit may serve multiple users, for example, in one building or in multiple adjacent buildings. Such applications typically require large bandwidths due to the large number of end users at one subscriber unit site.

The PHY ARQ deployed in these systems is transparent to higher layers such as the Medium Access Controller (MAC). As a result, PHY ARQ is available with respect to higher layer ARQ such as layer 2. In that case, PHY ARQ reduces the retransmission overhead of higher layer ARQ.

3 shows an example of an N channel stop and wait structure of the PHY ARQ 30. The physical layer (PHY) ARQ transmitter function 38 may be placed at the base station, the subscriber unit, or both depending on whether the downlink, uplink or both PHY ARQs are used. Block 34a of data arrives from the network. The network block is placed in a queue (queue) 34 for transmission over the data channel 41 of the air interface 43. The N channel sequencer 36 sequentially transmits block data to the N transmitters 40-1 through 40-n. Each transmitter 40-1 through 40-n is associated with a transmission sequence of data channel 41. Each transmitter 40-1 to 40-n performs FEC encoding on block data to provide ECS for the block data and to generate a packet for AMC modulation and transmission in the data channel 41. The FEC encoding / ECS data is stored in the buffers of the transmitters 40-1 to 40-n for possible retransmission. In addition, control information is transmitted from the PHY ARQ transmitter 38 to synchronize reception, demodulation, and decryption at the receivers 46-1 through 46-n.

N receivers 46-1 through 46-n each receive a packet in its associated time slot. The received packets are sent to individual hybrid ARQ decoders 50 (50-1 to 50-n). Hybrid ARQ decoder 50 determines the error rate for the received packet, such as BER or BLER. If the packet has an acceptable error rate, the packet is released to a higher level for further processing and an ACK is sent by the ACK transmitter 54. If the error rate is not acceptable or no packet is received, no ACK is sent or a NAK is sent. Packets with an unacceptable error rate are buffered at the decoder 50 which is likely to combine with the retransmitted packets.

A method for combining packets using a turbo code is as follows. If a turbo encoded packet is received at an unacceptable error rate, the packet data is retransmitted to facilitate code combining. Packets containing the same data are encoded differently. To decrypt the packet data, both packets are processed by the turbo decoder to recover the original data. Since the second packet is encoded differently, its soft symbols are mapped to different points in the decoding method. Using two differently encoded packets adds coding diversity and transmit diversity to improve the overall BER. In another method, the same signal is transmitted. The two received packets are combined using the maximum combining ratio of the symbols. The combined signal is sequentially decoded.

An ACK for each receiver 46-1 through 46-n is sent in a fast feedback channel (FFC) 45. The fast feedback channel 45 is preferably a low latency channel. In a time division redundancy system, ACK can be transmitted in idle time between upstream transmission and downstream transmission. The FFC 45 is preferably a low speed, high bandwidth CDMA channel that overlaps other in-band transmissions. Select FFC CDMA code and modulation to minimize interference to other in-band transmissions. Multiple codes may be used to increase the capacity of this FFC 45.

The ACK receiver 56 detects the ACK and indicates to the corresponding transmitters 40-1 to 40-n whether the ACK has been received. If no ACK is received, the packet is retransmitted. The retransmitted packet may have different modulation and encoding methods as indicated by the AMC controllers 12c and 26c. When an ACK is received, the transmitters 40-1 through 40-n clear the previous packet from the buffer and accept the subsequent packet for transmission.

The number N of transmitters and receivers is based on various design considerations, such as channel capacity and ACK response time. For the good system described above, a two-channel structure with odd and even transmitters and receivers is used well.

The PHY ARQ technique of the preferred embodiment provides a gain of 7 db in signal-to-noise ratio (SNR) compared to a system using only upper layer ARQ. This occurs by using a smaller block size for layer 1, which is more practical when operating at high block error rate (BLER) (5-20% BLER) and using only upper layer ARQ. Reduced SNR requirements enable: That is, switching to higher-order modulation using adaptive modulation and coding (AMC) technology increases capacity and uses low-grade RF (high frequency frequency) components with PHY ARQ to compensate for reduced implementation performance. CPE) can be implemented at low cost, increase downlink range to extend cell radius, reduce downlink power of base station (BS) to minimize cell-to-cell interference, and power amplifier when using multi-carrier technology It is possible to increase the back-off of PA.

1A and 1B are schematic block diagrams of a downlink and uplink physical layer automatic retransmission request (ARQ).

2 is a flow diagram using retransmission statistics for adaptive modulation and coding.

3 is a block diagram illustrating a multi-channel stop and wait structure.

Claims (23)

A base station (BS) that implements an automatic repeat request (ARQ) of a physical layer (PHY) and includes a transmitter and a receiver, Receive the data, format the received data into a packet with a particular data encoding / modulation, transmit the packet, and reply the packet in response to a failure to receive a corresponding acknowledgment (ACK) for a given packet. A physical layer transmitter for retransmitting; An ACK receiver for receiving the corresponding acknowledgment; An adaptive modulation and encoding controller that collects retransmission statistics and adjusts the specific data encoding / modulation using the collected statistics; A physical layer receiver for demodulating the received packet; A combiner / decoder for buffering, decoding, and detecting packet errors; ACK generator for generating a positive response for each packet if the packet has an acceptable error rate A base station comprising a. 2. The base station of claim 1 wherein the specific data encoding / modulation is forward error correction (FEC). 3. The method of claim 2, wherein the packet is transmitted using an orthogonal frequency division multiple access (OFDMA) air interface, and specific data encoding / modulation adjustment of the forward error correction (FEC) is performed by selecting subchannels in the OFDMA scheme set. A base station that is implemented in addition to red nulling. 2. The base station of claim 1, wherein the packet is transmitted using an air interface of Single Carrier-Frequency Domain Equalization (SC-FDE). The base station of claim 1, wherein the base station uses a code division multiple access (CDMA) air interface, and the acknowledgment is transmitted on a fast feedback channel. The base station of claim 1, wherein the ACK generator sends a negative acknowledgment (NAK) when any packet has an unacceptable error rate. In the physical layer automatic retransmission request apparatus used in the base station, Means for receiving data, Means for formatting the received data into packets for transmission with specific data encoding / modulation; Means for transmitting the packet, Means for retransmitting a packet if no acknowledgment (ACK) is received for the packet, Means for collecting retransmission statistics, and Means for adjusting each particular data encoding / modulation using the collected retransmission statistics With a transmitter comprising: Means for receiving a packet, Means for decrypting each received packet by error checking, and Means for generating an acknowledgment at the physical layer if the received packet has an acceptable error rate Receiver including Physical layer automatic retransmission request device comprising a. 8. The apparatus of claim 7, wherein the specific data encoding / modulation is forward error correction (FEC). 8. The method of claim 7, wherein the packet is transmitted using an orthogonal frequency division multiple access (OFDMA) air interface, and specific data encoding / modulation adjustment of the forward error correction (FEC) is performed by selecting subchannels in the OFDMA set. A physical layer automatic retransmission request device that is implemented in addition to red nulling. 8. The apparatus of claim 7, wherein the packet is transmitted using an air interface of a single carrier frequency domain equalization (SC-FDE) scheme. 8. The apparatus of claim 7, wherein the acknowledgment is transmitted on a fast feedback channel using a code division multiple access (CDMA) air interface. 8. The apparatus of claim 7, wherein the means for generating an acknowledgment generates a negative response if any packet has an unacceptable error rate. A base station supporting broadband wireless communication, A sequencer having a queue for receiving data blocks from the communication network and sequentially delivering packets to the n transmitters; N transmitters for transmitting said packet over a data channel; N receivers for receiving a feedback packet on the data channel; N hybrid ARQ decoders each coupled with the n receivers Including, The n hybrid ARQ decoders include a feedback channel for transmitting an acknowledgment (ACK) and for releasing packets with an acceptable error rate when any packet having an acceptable error rate is received. Base station. 14. The receiver of claim 13, wherein the n transmitters each temporarily store a packet transmitted in a buffer memory, and wherein the n transmitters receive an acknowledgment (ACK) signal for the stored packet at one of the n receivers. And a base station supporting broadband wireless communication when clearing the stored packet in preparation for receiving another block. 15. The apparatus of claim 13, wherein the n transmitters each temporarily store packets transmitted in a buffer memory, and wherein each of the n transmitters has an acknowledgment (ACK) signal for the stored packets of one of the n receivers. And retransmit packets temporarily stored in the buffer memory when they are not received at the receiver. 14. The base station of claim 13, wherein each of the n transmitters clears the buffer memory when the acknowledgment signal has not been received after the maximum number of retransmissions. 17. The base station of claim 16 wherein each maximum number of retransmissions is an integer value defined by an operator in the range 1-8. 14. The base station of claim 13, wherein each of the n receivers combines the retransmitted packet with the original transmitted packet to facilitate error correction. 14. The base station of claim 13, wherein a transmitter that fails to receive an acknowledgment signal encodes the packet by using a coding technique different from the coding technique used for the original transmission of the packet. 14. The broadband wireless communication of claim 13, wherein each of the n transmitters uses turbo encoding and the n hybrid ARQ decoders use a code combination of original transmission and retransmission to facilitate error correction. Support base station. 15. The wideband wireless communication of claim 13, wherein the packet is transmitted using an orthogonal frequency division multiple access (OFDMA) air interface, wherein frequency subchannels in the OFDMA set can be selectively nulled. Base station. 14. The base station of claim 13, wherein the packet is transmitted using an air interface of a single carrier frequency domain equalization (SC-FDE) scheme. 14. The base station of claim 13, wherein the acknowledgment is transmitted on a fast feedback channel using a code division multiple access (CDMA) air interface.

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